Dynamic seals are those which act to control fluid leakage between two surfaces which slide against one another. Such seals are quite common and include face seals for pumps, ship propeller shafts, compressors and appliances, lip seals for oil and grease, packings for pistons and piston rods, and piston rings for engines and compressors. Performance of existing sealing devices frequently imposes limits on the reliability, life and efficiency of machines requiring their use. Indeed, many sealed bearings fail in service due to failure of a dynamic seal therein. Process industries spend a good deal of time and money maintaining and replacing dynamic seals in their equipment.
Most dynamic seals suffer from two limitations. First, the seal typically wears out faster than the rest of the machine of which it forms a part. Second, the seal intrinsically contributes significantly to the frictional load of the machine in which it functions. These limitations occur because a dynamic seal comprises two surfaces or faces squeezed together which slide against each other during the operation of the machine of which it is a part. In many cases, lubrication of the seal during the time the faces are sliding against each other is poor at best.
Recent advances in seal and bearing technology have primarily been addressed to improved materials, such as materials having a higher hardness, materials with improved resistance to heat and corrosion and materials which use polymers. Improvements have also been made in the geometry of seals. For example, waviness and radial taper have been used in face seals and various types of grooves have been used on lip seals. U-cup, V-wedge and slipper seal designs have been used in packings.
Other seals and bearings have been developed having "peaks" and "valleys" on the sliding surfaces to enhance lubrication. Otto, in U.S. Pat. No. 3,572,730, entitled WEAR SURFACE FOR FACILITATING LUBRICATION OF ELEMENTS IN ENGAGEMENT THEREWITH and U.S. Pat. No. 3,586,340, entitled WEAR SURFACE AND SEAL CONSTRUCTION, and in SAE Transactions, Vol. 83, 1974, entitled "Triangular Asperities Control Seal Leakage and Lubrication," teaches the use of lithographic or photographic techniques to provide a bearing surface which has a geometric array of large size triangular asperities. The surfaces are then coated with plastic so that the voids surrounding the asperities are filled with plastic. The plastic then preferentially wears during operation exposing the triangular asperities. Otto does not teach differential roughness or providing load support across the entire surface.
Others teach the use of alternating hard and soft surface materials to provide various useful characteristics as disclosed in the following U.S. Pat. Nos.: 4,474,861, entitled COMPOSITE BEARING STRUCTURE OF ALTERNATING HARD AND SOFT METAL, AND PROCESS FOR MAKING THE SAME, to Ecer; 1,637,317, entitled BEARING, to Shoemaker; 3,235,316, entitled JOURNAL BEARING WITH ALTERNATING SURFACE AREAS OF WEAR RESISTANT AND ANTI-GALLING MATERIALS, to Whanger; 2,971,248, entitled COMPOSITE BEARINGS AND METHOD OF FORMING THE SAME, to Kingsley, et al.; 2,268,869 entitled BEARING MEMBER, to Given; 356,331, entitled ANTI FRICTION JOURNAL BEARING, to Randolph; 4,562,122, entitled MULTI-LAYER PLAIN BEARING, to Hodes, et al. (see FIG. 3 of Hodes); 3,656,823, entitled SLIDABLE CARRIER OR SUPPORT, to Tiraspolsky, et al.; 3,961,104, entitled INTERNAL CYLINDRICAL BEARING SURFACES, to Tanner; and 3,075,816, entitled BEARINGS FOR RELATIVELY ROTATING MEMBERS, to Harris, et al. None of these references disclose differential roughness, differential wear or providing load support across the entire surface.
One relatively unexplored approach to improving seal life and efficiency is to control the microgeometry or microtopography, i.e., the geometric variations in surface roughness, which establish lubricating fluid film height variations of the seal face. The present invention addresses this approach utilizing a bearing comprising a surface having regions which, as they wear, yield different amounts of surface roughness which still provides asperity tip load support. Ancillary to this, and in conjunction therewith, the wear rate of the surface regions in combination with the surface roughness may be controlled during the use and consequently during the wear of the bearing surface. Bearings and seals in accordance with the invention have enhanced load support and lubrication characteristics, and control fluid leakage by utilizing surfaces having regions of differential roughness. By utilizing differential roughness, different regions of the bearing surface develop different effective film thicknesses, thereby controlling hydrodynamic and hydrostatic pressures.